Ultrasonographic detection of venous and arterial nitrogen bubbles will be performed in divers after surfacing from simulated dives in hyperbaric chambers. Divers will be observed after two different dive profiles - Dive A (dive to 18 m for 80 min bottom time) and dive B (dive to 50 m for 20 min bottom time), both performed according to US Navy Air decompression procedure 1996. For both dives two groups will be compared: Divers with PFO and divers after previous catheter-based closure of PFO.